This decline has been linked to reduced intake of 'host foods' including tea, coffee, and cereal, as well as the growth of the plant-based milk sector.
The pro-dairy AHDB pointed out that while more people are opting for vegan milk alternatives, in terms of volume, they currently account for just 4.6 percent of UK milk sales.
In addition, it said 98.5 percent of UK households still buy liquid milk, and other dairy products - for example cheese - are seeing growth in consumption.
The release of the data corresponds with the dairy industry's 'Februdairy' campaign - an attempt to emulate the success of Veganuary by promoting dairy products online.
The success of the campaign - which has been largely hijacked by vegan activists, using the hashtag to highlight ethical and environmental issues around dairy - has been questioned by some.
According to vegan charity Viva!: "Although the industry admits it needs a re-brand, it seems to be in denial about why people are ditching dairy for plant-based alternatives.
"Until dairy advocates understand this, it looks like we'll be seeing a lot more Februdairy-style campaigns from the industry as veganism continues to grow globally."
In a further bid to tackle changing consumer tastes, AHDB will re-launch its 'Department of Dairy Related Scrumptious Affairs' digital marketing campaign, which it funds jointly with UK. The campaign predominantly targets young people, as they are the most likely to switch to plant-based alternatives.
Rebecca Miah, head of dairy marketing at AHDB, said: "The campaign aims to remind people of their love of dairy and address the attitudes affecting overall dairy consumption. By targeting millennials and new parents, many of which are open to considering alternatives, we are influencing the next generation.
"The Department has run for the past two years with strong results – an 11 percent increase in those certain to buy dairy, an 11 percent drop in those planning to switch into alternatives and an eight percent drop in those planning to cut down their dairy intake in the future.
"AHDB also runs various programmes of activity defending dairy in the reputational areas of animal welfare and environment, which contributes to the overall success of the Department and the ultimate positive attitude shifts."